1. Field of the Invention
The subject invention relates to the field of plastic fabrication and, more particularly, to a method for forming a deep draw polypropylene spa shell.
2. Description of Related Art
In the prior art, portable spa shells have been fabricated from a variety of materials, including fiberglass-reinforced polyester, acrylic, ABS, and vinyl. The spa shell forms the tub which holds the heated water and attendant chemicals. The combination of hot chlorinated water and the poorly controlled chemical balance encountered in the typical spa environment attacks and damages conventionally-used shell materials.
The inventors have recognized that polypropylene is a material which is highly resistant to damage and deterioration by typical spa environments, particularly when compared to other plastics. They have further recognized that polypropylene could also provide a first class visual appearance.
A number of obstacles confront any effort to construct a spa shell from polypropylene, including the requirement to "deep draw" the material to form tub depths of, for example, 27 inches. Additionally, polypropylene repels the various foam materials typically employed to insulate the spa shell. As opposed to other plastics, polypropylene is a crystalline material and has a narrow temperature window of formability which presents obstacles to forming the various functional areas of a spa tub, as well as achieving the deep draw necessary to form such a tub.